1. Field of the Invention
The present invention relates to an imaging apparatus equipped with an anti-shake (image shake correction/image stabilizing/shake reduction) system.
2. Description of the Related Art
In recent years, mobile electronic devices which are designed mainly for taking still/moving photographic images, such as digital cameras (still-video cameras) and digital camcorders (motion-video cameras), and other mobile electronic devices which are designed to be capable of taking such photographic images as a subsidiary function, such as mobile phones equipped with a camera and personal digital assistants (PDAs) equipped with a camera, have become widespread. In these types of mobile electronic devices, it is common to provide the mobile electronic device therein with an imaging unit (imaging apparatus) which is configured so that an image sensor (image pickup device) and an imaging optical system, for guiding light emanating from a photographic object (object-emanated light) to the image sensor, are accommodated in a hollow housing of the imaging unit. Additionally, in recent years, the demand to slim down this type of imaging unit has become stronger due to further progress in the slimming down of mobile electronic devices. In order to slim down an imaging unit, it is known to provide an imaging unit with a bending optical system which reflects (bends) light rays using a reflecting surface of a reflector such as a prism or a mirror.
In addition, there tends to be a demand for imaging units to be equipped with a so-called anti-shake (image shake correction) system that is designed to reduce image shake on an image plane that is caused by vibrations such as hand shake. The following four different types of imaging units are known in the art as imaging units using a bending optical system which are equipped with an anti-shake system: a first type (disclosed in Japanese Unexamined Patent Publication Nos. 2009-86319 and 2008-268700) in which an image sensor is moved in directions orthogonal to an image plane to reduce image shake, a second type (disclosed in Japanese Unexamined Patent Publication No. 2010-128384 and Japanese Patent No. 4,789,655) in which a lens disposed behind a reflector (on the image plane side) that has a reflecting surface is moved in directions orthogonal to an optical axis to reduce image shake, a third type (disclosed in Japanese Unexamined Patent Publication Nos. 2007-228005, 2010-204341, 2006-330439, and Japanese Patent No. 4,717,529) in which the angle of a reflector (a reflecting surface thereof) and the angle of a lens adjacent to the reflector are changed to reduce image shake, and a fourth type (disclosed in Japanese Unexamined Patent Publication Nos. 2006-166202 and 2006-259247) in which an entire imaging unit is tilted/inclined to reduce image shake.
An anti-shake system using voice coil motors (VCMs), which generate force (driving force) by application of a current (voltage) across the terminals of the coil positioned inside the magnetic field of a permanent magnet, for driving an optical element (anti-shake optical element) to reduce image shake is known in the art (disclosed in in Japanese Unexamined Patent Publication Nos. 2009-86319, 2010-128384, 2007-228005, and Japanese Patent No. 4,789,655). Information on the position of the anti-shake optical element can be obtained with sensors (Hall sensors) that measure the change in the magnetic field.
The first type of anti-shake system tends to become complicated in structure and tends to increase in cost because a circuit board connected to the image sensor is moved so as to follow movements of the image sensor, which requires electrical components around the image sensor also to be movable components in addition to the image sensor. In addition, the periphery of the imaging surface of the image sensor is required to be dust tight; however, in small imaging units intended for being incorporated into a mobile phone or a personal digital assistant, it is difficult to secure sufficient space for allowing the image sensor to perform an anti-shake (image shake correction/image-stabilizing/shake reduction) operation while maintaining the dust-tight structure of the image sensor.
The second type of anti-shake system has a structure such that the moving direction of the lens group, disposed behind the reflector, during an anti-shake operation corresponds to the direction of the thickness of the imaging unit (i.e., the forward/rearward direction of the imaging unit, wherein the direction toward an object to be photographed refers to the forward (front) direction of the imaging unit), and hence, there is a problem with providing enough space to house such an anti-shake structure in a slimmed-down imaging unit. In other words, the slimming of the imaging unit is limited if this type of anti-shake system is used. There is a similar problem also in the type of anti-shake system in which an image sensor is moved, instead of a lens group, in the direction of the thickness of the imaging unit.
The third type of anti-shake system requires a large space for allowing the reflector and the lens group to tilt/incline, and accordingly, the imaging unit is easily enlarged in size. The fourth type of anti-shake system requires a larger space for allowing the entire imaging unit to be tilted/inclined to reduce image shake.
Accordingly, there has been a demand for an anti-shake system that utilizes a different manner of driving an anti-shake optical element from those of the above described types of imaging units and that is advantageous for miniaturization and slimming of the imaging apparatus. In addition, in the case where voice coil motors are used as drive sources of an anti-shake system, a space-efficient arrangement of various elements of the anti-shake system such as permanent magnets, coils and sensors is also an important factor for miniaturization of the imaging apparatus in addition to the manner of driving the anti-shake optical element.
Voice coil motors that produce linear movement can transmit power without a mechanism for converting rotational motion to linear motion, so that the structure of an anti-shake system which moves an anti-shake optical element in a plane orthogonal to an optical axis of an imaging optical system can be easily simplified if voice coil motors are used for this anti-shake system. On the other hand, since permanent magnets and coils which constitute elements of voice coil motors are flat in shape, having a wide surface along a plane (plane orthogonal to an optical axis passing through the anti-shake optical element) in which the anti-shake optical element moves, the installation space for the permanent magnets and coils in the aforementioned plane tends to be large. Specifically, in voice coil motors for reducing image shake, two sets of permanent magnets and coils, the directions of linear movement of which are orthogonal to each other, are used and arranged around the anti-shake optical element; hence, attention must be paid to the arrangement of the voice coil motors in the case of miniaturization or slimming of an imaging unit which incorporates an anti-shake system using voice coil motors as drive sources thereof.
In addition, when moving magnet voice coil motors, in which permanent magnets are installed onto a member which is driven to reduce image shake, are used for an anti-shake system, there is a possibility of magnetic materials around the anti-shake system influencing the magnetic fields of the permanent magnets and deteriorating the driving accuracy of the anti-shake system, so that countermeasures for this problem are required.